Merge branch 'mainstream'

[sliver-openvswitch.git] / FAQ

diff --git a/FAQ b/FAQ
index e6e649f..c6ccbd1 100644 (file)
--- a/FAQ
+++ b/FAQ
@@ -1122,7 +1122,8 @@ A: Before version 1.11, Open vSwitch did not support MPLS.  That is,
    for MPLS.  With the userspace datapath only, these versions can
    match, push, or pop a single MPLS label, but they still cannot look
    past MPLS labels (even after popping them) into the encapsulated
-   packet.  Kernel datapath support is unchanged from earlier verions.
+   packet.  Kernel datapath support is unchanged from earlier
+   versions.
 
    Open vSwitch version 2.2 will be able to match, push, or pop up to
    3 MPLS labels.  Looking past MPLS labels into the encapsulated
@@ -1402,9 +1403,9 @@ A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
    even be convenient, e.g. it is often the desired behavior in a flow
    that forwards a packet to several ports ("floods" the packet).
 
-   Sometimes one really needs to send a packet out its ingress port.
-   In this case, output to OFPP_IN_PORT, which in ovs-ofctl syntax is
-   expressed as just "in_port", e.g.:
+   Sometimes one really needs to send a packet out its ingress port
+   ("hairpin"). In this case, output to OFPP_IN_PORT, which in
+   ovs-ofctl syntax is expressed as just "in_port", e.g.:
 
        ovs-ofctl add-flow br0 in_port=2,actions=in_port
 
@@ -1474,6 +1475,23 @@ A: These flows drop the ARP packets that IP hosts use to establish IP
       priority=5,in_port=1,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=2
       priority=5,in_port=2,dl_dst=01:00:00:00:00:00/01:00:00:00:00:00,actions=1
 
+
+Development
+-----------
+
+Q: How do I implement a new OpenFlow message?
+
+A: Add your new message to "enum ofpraw" and "enum ofptype" in
+   lib/ofp-msgs.h, following the existing pattern.  Then recompile and
+   fix all of the new warnings, implementing new functionality for the
+   new message as needed.  (If you configure with --enable-Werror, as
+   described in INSTALL, then it is impossible to miss any warnings.)
+
+   If you need to add an OpenFlow vendor extension message for a
+   vendor that doesn't yet have any extension messages, then you will
+   also need to edit build-aux/extract-ofp-msgs.
+
+
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